1. Field of the Invention
The disclosed invention relates to devices for the measurement of elevated temperatures and/or fevers in animals, particularly cattle.
2. Prior Art
For quite some time there has existed an unsolved need to determine when farm animals are sick without having to inspect each animal manually at regular intervals. Since a high percentage of sick animals have detectable fevers, an effective way of identifying such animals is to measure the body temperature of all the animals and to look for abnormally high temperatures. Although multiple schemes to monitor automatically the health of animals have been pursued by various companies, inventors, and research laboratories, each scheme eventually proved itself to be either uneconomical, unworkable, or both.
The detection of fever in animals can pose a special problem due to the fact that the normal, healthy internal temperature of an animal may vary with ambient temperature. In addition, of course, a device for detecting a fever in an animal must be small, inexpensive, have a reasonable operational life, with low power consumption, and have a useful transmission range.
U.S. Pat. No. 3,070,773 issued to Woolston, et al. describes a device which transmits ambient temperature information as well as internal temperature information using a frequency-modulation technique. The described device, although useful in circumstances such as those for which the present invention is designed, requires an uneconomical, large amount of power because it is always powered up and active when an individual signal such as the internal temperature signal is present. It does not directly indicate the presence of a fever in the cow because it does not account for or indicate changes in fever temperatures when ambient temperatures are high. Further, the disclosed system does not provide any means of identifying which particular animal in a large herd is the one with the fever.
U.S. Pat. No. 3,781,837 describes a device which transmits an alarm when an individual cow in a herd has a fever. The device described has a thermistor-based ambient temperature compensating circuit so that an alarm is triggered only when the internal temperature is about 40.degree. C. when ambient temperatures are below about 38.degree. C., or above 0.degree. C. when ambient temperature is above about 38.degree. C. However, this device continuously monitors temperature and generates a continuous alarm signal when an alarm condition is sensed; as a result, it continuously draws power and utilizes such a large amount of power that it is not economical. Again, such a device does not provide an automatic means for identifying which particular animal in a herd is the one with the fever.
U.S. Pat. No. 4,075,632 describes a device which acquires the energy to take a temperature reading only upon receipt of radiation emitted from an "interrogator"; it is not battery powered and does not operate independently of the separate interrogator. When the device is energized it transmits a temperature reading but does not compensate for the increase of internal temperature due to increased ambient temperature. Although it does provide identification number encoding which makes it clear which animal is emitting the signal, the method of powering the device with the "interrogator" limits the transmitting range of the devices to where they are of little practical use. In addition, the complexity and amount of circuitry in the devices makes the system prohibitively expensive.
Because other previous schemes have used infrared or sound to communicate temperature information or the health of an animal, either human observers have had to be present to hear the alarm or the infrared beam could only be received when the animal had its head in a given orientation.